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Message: <blockquote data-quote="Mark FX" data-source="post: 1407947" data-attributes="member: 211556">The old fashioned way to do synthesized properties, was to declare an instance variable with the same name as the property like this.[CODE]//myClass.h#import <UIKit/UIKit.h>@interface myClass : NSObject{        double topSpeed;}@property (nonatomic, readwrite, assign) double topSpeed;@end//myClass.m#import "myClass.h"@implementation myClass@synthesize topSpeed;@end[/CODE]By default, a synthesized property will access the instance variable of the same name, so the topSpeed property will access the topSpeed instance variable, and the setter and getter methods will also set or return the instance variable's value.But the latest trend with using synthesized properties, is to let the @sythensize command automatically create an instance variable of the same name for you, which is what it does if you have not created one yourself.So the above code can be written like this.[CODE]//myClass.h#import <UIKit/UIKit.h>@interface myClass : NSObject@property (nonatomic, readwrite, assign) double topSpeed;@end//myClass.m#import "myClass.h"@implementation myClass@synthesize topSpeed;@end[/CODE]Which will automatically create an instance variable for you called topSpeed.Then suppose, you want to change the name of the automatically created instance variable to a different name,  then you would do this.[CODE]//myClass.h#import <UIKit/UIKit.h>@interface myClass : NSObject@property (nonatomic, readwrite, assign) double topSpeed;@end//myClass.m#import "myClass.h"@implementation myClass@synthesize topSpeed = carTopSpeed;@end[/CODE]This means that you would get an set the topSpeed property and created instance variablewith this code.[CODE]        carsTopSpeed = 120.00;        NSLog(@"topSpeed = %f", carsTopSpeed)"[/CODE]So in trying to awnser your question, all of the above code snippets are valid, but the last isa way of you using a different instance variable name for your synthesized properties.Apple's prefered instance variable prefix is to use an undersore "_", and also the Xcode project templates are set to also use the underscore "_" prefix, for any properties it creates for it's projects.A good reason for using the underscore prefix, is when your creating user interface properties, like windows buttons or text fields, so that when your writing your code, you don't get naming conflicts with commonly used words, and class message commands, like this.[CODE]@synthesize window = _window;- (void)displayWindow{        [_window makeKeyAndVisible];}[/CODE]Hope this is of some help.Regards Mark</blockquote>

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